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Beskrivelse
Ecological explanations for the distribution of organisms involve several interrelated ideas. First is the idea of populations, which is the subject of analytical biogeography. Each species has a characteristic life history, reproduction rate, behaviour, means of dispersion, and so on. These traits affect a population's response to the environment in which it lives. The second idea concerns this biological response to the environment and is the subject of ecological biogeography. A population responds to its physical surroundings (abiotic environment) and its living surroundings (biotic environment). Factors in the abiotic environment include such physical factors as temperature, light, soil, geology, topography, fire, water, water and air currents; and such chemical factors as oxygen levels, salt concentrations, the presence of toxins, and acidity. Factors in the biotic environment include competing species, parasites, diseases, predators, and humans. In short, each species can tolerate a range of environmental factors. It can only live where these factors lie within its tolerance limits. This insect (Arphia conspersa) ranges from Alaska and northern Canada to northern Mexico, and from California to the Great Plains. It is found at less than 1,000 m elevation in the northern part of its range and up to 4,000 m in the southern part. Within this extensive latitudinal and altitudinal range, its istribution pattern is very patchy, owing to its decided preference for very specific habitats. It requires short-grass prairie, or forest and brushland openings, peppered with small pockets of bare ground. Narrow-leaved grasses provide the grasshopper's food source. The bare patches are needed for it to perform courtship rituals. These ecological and behavioural needs are not met by dense forest, tall grass meadows, or dry scrubland. Roadside meadows and old logged areas are suitable and are slowly being colonized. Moderately grazed pastures are also suitable and support large populations.